<%@ Page Language="VB" AutoEventWireup="True" %>
<%@ Import Namespace="System.Data" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<script runat="server">
' Normally, an entire data source is loaded in the DataGrid control,
' which can take up a lot of resources. This example uses custom
' paging, which loads only the segment of data needed to fill a
' single page. In order to query for the appropriate segment of
' data, the index of the first item displayed on a page must be
' tracked as the user navigates between pages.
Dim startIndex As Integer = 0
Function CreateDataSource() As ICollection
' Create sample data for the DataGrid control.
Dim dt As DataTable = New DataTable()
Dim dr As DataRow
' Define the columns of the table.
dt.Columns.Add(New DataColumn("IntegerValue", GetType(Int32)))
dt.Columns.Add(New DataColumn("StringValue", GetType(String)))
dt.Columns.Add(New DataColumn("DateTimeValue", GetType(String)))
dt.Columns.Add(New DataColumn("BoolValue", GetType(Boolean)))
' Populate the table with sample values. When using custom paging,
' a query should only return enough data to fill a single page,
' beginning at the start index.
Dim i As Integer
For i = startIndex To ((startIndex + MyDataGrid.PageSize) - 1)
dr = dt.NewRow()
dr(0) = i
dr(1) = "Item " & i.ToString()
dr(2) = DateTime.Now.ToShortDateString()
If (i Mod 2 <> 0) Then
dr(3) = True
Else
dr(3) = False
End If
dt.Rows.Add(dr)
Next i
Dim dv As DataView = New DataView(dt)
Return dv
End Function
Sub Page_Load(sender As Object, e As EventArgs)
' Load sample data only once, when the page is first loaded.
If Not IsPostBack Then
' Set the virtual item count, which specifies the total number
' items displayed in the DataGrid control when custom paging
' is used.
MyDataGrid.VirtualItemCount = 200
' Retrieve the segment of data to display on the page from the
' data source and bind it to the DataGrid control.
BindGrid()
End If
End Sub
Sub MyDataGrid_Page(sender as Object, e As DataGridPageChangedEventArgs)
' For the DataGrid control to navigate to the correct page when
' paging is allowed, the CurrentPageIndex property must be updated
' programmatically. This process is usually accomplished in the
' event-handling method for the PageIndexChanged event.
' Set CurrentPageIndex to the page the user clicked.
MyDataGrid.CurrentPageIndex = e.NewPageIndex
' Calculate the index of the first item to display on the page
' using the current page index and the page size.
startIndex = MyDataGrid.CurrentPageIndex * MyDataGrid.PageSize
' Retrieve the segment of data to display on the page from the
' data source and bind it to the DataGrid control.
BindGrid()
End Sub
Sub BindGrid()
MyDataGrid.DataSource = CreateDataSource()
MyDataGrid.DataBind()
End Sub
</script>
<head runat="server">
<title> DataGrid Custom Paging Example </title>
</head>
<body>
<form id="form1" runat="server">
<h3> DataGrid Custom Paging Example </h3>
<asp:DataGrid id="MyDataGrid"
AllowCustomPaging="True"
AllowPaging="True"
PageSize="10"
OnPageIndexChanged="MyDataGrid_Page"
runat="server">
<HeaderStyle BackColor="Navy"
ForeColor="White"
Font-Bold="True" />
<PagerStyle Mode="NumericPages"
HorizontalAlign="Right" />
</asp:DataGrid>
</form>
</body>
</html>

Remarks

Paging allows you to display the contents of the DataGrid control in page segments. The number of items on a page is determined by the PageSize property. If no value is specified for the PageSize property, the DataGrid will display 10 items on a page.

Normally, a data source that contains every row in the DataGrid control is loaded every time the DataGrid control moves to a different page. This can consume a lot of resources when the data source is very large. Custom paging allows you to load just the segment of data needed to display a single page.

The event handler receives a DataGridPageChangedEventArgs object as a parameter. You can use the NewPageIndex property of this parameter to determine the index of the page selected by the user from the page selection elements of the DataGrid control.

Next, create a data source that contains the data to display on a single page and then use the DataBind method to bind the data to the DataGrid control.

Note

Because only a segment of the data is loaded, you must set the VirtualItemCount property to the total number of items in the DataGrid control. This allows the control to determine the total number of pages needed to display every item in the DataGrid control. This property is normally programmatically set once the total number of items in the DataGrid control is determined.

When paging is enabled with the AllowCustomPaging property is set to false, the DataGrid control assumes that the data source contains all the items to be displayed. The DataGrid control calculates the indexes of the items on the displayed page based on the page index, specified by the CurrentPageIndex property, and the number of items on a page, specified by the PageSize property.

When the AllowCustomPaging property is set to true, the DataGrid control assumes that the data source only contains the items as determined by the VirtualItemCount property. All items up to the number of items specified by the PageSize property are displayed.